Having just finished Spec Ops: The Line, I have to mention a game that has a similarly gripping story.
Second Sight is available on steam and has one of the deepest stories in any game I have ever played, it is by far the deepest for its rating, although it is rated T, and a hard T at that, some blood/language/horror.
I wont mention the story, don't read anything about the story, even if you don't plan on getting the game, you might find it for free somehow and will regret spoiling it.
The main problem with the game is that it wasn't ported well to the PC, the controls are setup for a gamepad and the video options are limited. However, it is playable on Windows 7 and I got used to it rather quickly. The game is on PS2 also but it would probably be more expensive than just buying it off steam.
The only game I can really think of that meets your rules is Psychonauts, its not super profound but it is deep.